We report the high-performance circuit on 25-μm polyimide substrate with organic thin-film transistors (TFTs) (OTFTs) using 6,13-bis(triisopropyl-silylethynyl) pentacene and polymer blending. Because of high mobility (0.64 cm2/V·s) and low threshold voltage (<;|1 V|) of the TFTs, an 11-stage ring oscillator (RO) made of these TFTs exhibits the switching speed of 31.4 kHz at the supply voltage of 20 V. The output waveforms of the RO change little after 5000 times bending with a radius of curvature of 2 mm, and thus, the OTFT circuits can be applied to very flexible electronics.